Study on optical properties and upconversion luminescence of K2YF5:Sm3+ single crystals

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy was employed to study the luminescence properties of hexagonal boron nitride (h-BN) crystal powders after annealing the samples at different temperatures in the range of 100–900 °C for 1 h in ambient air. The PL spectrum from the h-BN powder samples annealed around 700 °C showed strong luminescence intensity at 5.49 eV along with enhanced phonon-assisted band-edge emission at 5.90 eV. Additionally, it revealed sharp atomic-like emission lines in UV region at 4.10, 4.12, 4.14, and 4.16 eV with line widths less than 1 nm from the annealed samples which were not present in the unannealed samples. Power- and temperature-dependent PL measurements of the sharp atomic-like emission lines exhibited robust nature of the energy peak positions. Based on the theoretical reports, the sharp emission lines could be carbon-related defects.

Visible up-conversion luminescence in Er 3+-doped PbWO 4 single crystals

Study on upconversion luminescence and thermal properties of Ho3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glasses

Upconversion luminescence enhancement and color modulation in Yb3+/Er3+/Ln3+ (Ln = Tm, Ho) tri-doped YF3 microrods

Frequency upconversion (UC) luminescence in nanocrystalline zirconia (ZrO2) and hafnia (HfO2) doped with Er3+ and Yb3+ was studied under continuous-wave excitation at 980 nm. Samples of ZrO2:Er3+, ZrO2:Er3+/Yb3+, and HfO2:Er3+/Yb3+ were prepared by the sol-gel technique and characterized using x-ray diffraction and electron microscopy. A study of the infrared-to-green and infrared-to-red UC processes was performed including the analysis of the spectral and the temporal behavior. The mechanisms contributing to the UC luminescence were identified as excited state absorption and energy transfer among rare-earth ions.

The reported work in 2003-2019 on the reverse saturable absorption (RSA) or two-photon absorption (TPA) and/or optical limiting (OPL) of platinum(II) terpyridine complexes was summarized in this minireview. Photophysical properties, including the ground-state absorption (GSA), excited-state absorption (ESA), excited-state lifetimes, and the quantum yields of triplet excited-state formation, RSA/OPL at 532 nm for ns laser pulses, TPA characteristics in the near-IR spectral regions, and the structure-property correlations were reviewed. This paper is composed of four sections. First, the current status of OPL materials and devices, the general requirements for reverse saturable absorbers and two-photon absorbing materials, and the different types and characteristics of square-planar platinum(II) complexes were briefly introduced. Then the photophysics and RSA/OPL of six series of Pt(Ⅱ) terpyridine-analogous complexes and the structure-property correlations were discussed. Following it the TPA of five series of Pt(Ⅱ) terpyridine complexes and the impacts of structural variations on the TPA cross sections (σ2) were reviewed. Finally, brief conclusions were drawn based on the reported studies. A general trend discovered was that the charge transfer absorption band(s) and the ESA can be readily tuned by substituents on the acetylide or the terpyridine ligand. Introducing electron-donating substituent to the acetylide or terpyridine ligand or improving the coplanarity between the aromatic substituent and the terpyridine ligand red-shifted the ground-state charge-transfer absorption band(s) at the price of decreasing/quenching the triplet ESA, which consequently reduced the RSA/OPL at 532 nm. Extending the π-conjugation of the terpyridine ligand dramatically improved the σ2 values of the Pt(Ⅱ) terpyridine complexes. Incorporation of electron-withdrawing π-conjugated aromatic substituent restrained the GSA to < 500 nm while keeping a long-lived triplet excited state with broadband ESA in the visible spectral regions and moderately strong TPA in the NIR regions. This approach could provide a solution for developing broadband OPL materials.

The ultraviolet and violet upconverted luminescence around 320, 410, and 470 nm in ${\mathrm{Er}}^{3+}$-doped yttrium aluminum garnet has been observed at room temperature with a tunable OPO laser excitation. The upconversion mechanisms upon ${}^{4}{S}_{3/2}$ excitation $(\ensuremath{\approx}545 \mathrm{nm})$ are investigated by means of the decay profiles of upconvered luminescence and excitation spectrum. It appears that, depending on the excited wavelength, the upconverted luminescence is dominantly contributed either by energy-transfer upconversion or by excited-state absorption. The relative intensities of upconverted luminescence are discussed using Judd-Ofelt theory.

Tm3+/Er3+/Yb3+-codoped oxyhalide tellurite glasses as materials for three-dimensional display

The techniques of pulsed photoacoustic spectroscopy and multiphoton ionization spectroscopy have been used to study several types of weak optical transitions in the ultraviolet or visible spectral regions for gas phase molecules. Both one- and two-color experiments have been performed. The one-color experiments involved the study of high vibrational overtones and spin-forbidden transitions. The two-color experiments demonstrated the application of photoacoustic detection of stimulated emission pumping for populating high vibration levels of the ground electronic state. Two-color experiments were also used to study excited state absorption processes in aniline. Pulsed laser photoacoustic spectra of CD3H in the region of the ∇vCH = 5, 6, and 7 CH stretch overtones were obtained. These overtones and nearby combination bands displayed sharp rotational structure, indicating a minimum excited state population relaxation time of 5 x 10-12 sec. A combination sum analysis was used to generate excited state rotational constants B'. These constants reflect the geometries of the excited states, and therefore provide a sensitive probe of the mixing between various zero order excited states. Photoacoustic detection was used to monitor a stimulated emission pumping process in p-difluorobenzene. Using the A&#771;1B2u 5' state as an intermediate state, several vibrational levels of the ground electronic state were populated. The photoacoustic technique is an attractive alternative to other techniques because of its sensitivity, simplicity, and its ability to differentiate between stimulated emission pumping and excited state absorption. Time-resolved excited state absorption studies were performed on aniline using the multiphoton ionization and photoacoustic detection techniques. Signals from both of these techniques were measured as a function of the time delay between two laser pulses of different wavelength. The first pulse excited the S1 0-0 transition. The second pulse excited either S1 or a triplet state produced by intersystem crossing, depending on the time delay between pulses. Both ionization and dissociation processes were observed. By varying the conditions of excitation, it appears that a given amount of energy can be selectively channeled into either ionization or dissociation pathways. These results were explained using a simple Franck Condon factor model. The application of pulsed laser photoacoustic spectroscopy to the study of weak absorptions in the visible and ultraviolet spectral regions was investigated. Photoacoustic spectra of triplet states in CS2, SO2, biacetyl, and thiophosgene were obtained. An attempt to detect the a&#771;3B1u state in benzene, produced instead a two-photon spectrum of several Rydberg states. It was discovered that the sensitivity of the pulsed photoacoustic technique for extremely weak absorptions is limited by the increased probability of multiphoton absorption when high intensities are used. Finally, in two appendices, the detection of the a&#771;3A2 state in CS2 by the multiphoton ionization technique is presented. The CS2 study demonstrates the utility of the multiphoton ionization technique for detecting spin-forbidden transitions at high resulution and with great sensitivity.

Zinc phosphate glasses activated with Dy3+/Eu3+/Sm3+ and Tb3+/Eu3+/Sm3+ for reddish-orange and yellowish white phosphor applications

Up-conversion luminescence spectra of CaF2-SrF2-HoF3 single crystals were investigated upon excitation by laser radiation with a wavelength of 1940 nm to the 5I7 level of Ho3+ ions. The CaF2-SrF2-HoF3 single crystals were grown by the vertical directional crystallization method. For these excitation conditions, quantitative characteristics of the up-conversion luminescence of Ho3+ ions were determined: energy yield, chromaticity coordinates, and correlated color temperatures. The possibility of increasing the efficiency of solar cells due to the conversion of infrared radiation in CaF2-SrF2-HoF3 crystals was considered.

The dynamic variation of upconversion luminescence dependent on shell Yb3+ contents in NaYF4: Yb3+,Tm3+@NaYF4: Yb3+,Er3+ nanoparticles

Fabrication and comprehensive structural and spectroscopic properties of Er:Y2O3 transparent ceramics

Currently, developing luminescent materials for dual-mode optical thermometry has been becoming a rising topic, and concurrent temperature-sensitive optical parameters hold the key. Still, it is a serious challenge, since distinct activators are generally needed and energy transfer (ET) processes among activators inevitably occur, further leading to severe luminescence quenching. Herein, a spatial separation strategy is proposed for designing dual-phase glass ceramics (GCs) containing ZnGa2O4:Cr3+ and NaYF4:Yb3+,Er3+ nanocrystals (NCs) for dual-mode optical thermometry, in order to integrate diversified activators into one. Structural, morphological, and optical characterizations are examined to verify the partition of Cr3+ into ZnGa2O4 and Er3+ into the NaYF4 lattice in the dual-phase GC. Benefiting from such a spatial separation strategy, the adverse ET processes between Cr3+ and Er3+ could be cut off in the dual-phase GC, contributing to downshifting (DS) and upconversion (UC) luminescence. Furthermore, dual-mode optical thermometry is performed based on the lifetime of Cr3+ and fluorescence intensity ratio (FIR) of Er3+, with high relative sensitivities of 0.95% K-1@450 K and 1.24% K-1@303 K, respectively. It is evidenced that the dual-phase GC holds great potential for dual-mode optical thermometry, and this work also offers a prospective pathway for expanding the practical applications of GC luminescent materials.

Green and red upconversion luminescence in CeO 2:Er 3+ powders produced by 785 nm laser